1. Field of the Invention
The present invention relates to a subsea pipe attachment and receiving assembly for use in subsea pipeline repairs.
2. Description of the Prior Art
There are thousands of miles of pipelines laying on the seabed. Pipe laying technology permits pipelines to be laid in extremely shallow water depths to water depths of thousands of feet. A serious problem results when a subsea pipeline in deep water is damaged and in need of repair. A few examples of how a subsea pipeline can be damaged are by an object impacting the pipeline, an anchor dragging across the pipeline, or corrosion.
Typically, to repair a damaged submerged pipeline in the past, a couple of repair methods were available. One repair method required the damaged section of the pipeline to be recovered to the water surface and the necessary repairs were conducted on the deck of a vessel. After the repair was made the pipeline was lowered and repositioned on the seabed. This method was generally limited to small diameter pipelines in relatively shallow water. A second method involved conducting the repair in situ by divers, using either repair clamps or hyperbaric welding techniques. This method had also limitations related to water depth and pipeline size.
It is known to use a remotely operated vehicle (ROV) in deep water to sever and recover a submerged pipeline. U.S. Pat. No. 5,044,827 to Gray et al. discloses a method for severing and recovering a submerged pipeline. The ROV jets beneath a portion of the pipeline and then a deflated lift bag is lowered to the submerged pipeline. The deflated lift bag is positioned under the submerged pipeline and then inflated until a section of the pipeline has been raised off of the seabed. A cut-off saw is lowered to the raised section of the pipeline. The cut-off saw is clamped to the pipeline prior to severing the pipeline. The cut-off saw is then removed from the severed pipeline. A recovery head is lowered to the raised end of the severed pipeline and after alignment is placed in the raised end of the severed pipeline. The recovery head is activated to establish a gripping relationship with the pipeline. A recovery cable is lowered and connected to the recovery head. The recovery cable is retrieved to recover the recovery head and the pipeline to the water surface.
As the offshore pipeline industry continues to venture into deeper and deeper waters, more and more pipelines of increasing diameter are being laid in water depths beyond the range of divers. Due to a variety of factors such as pipeline size, seabed bearing capacity, sea currents, and lay barge daily rates, a reliable and dependable method for repairing submerged pipelines without retrieval to the water surface is needed. The method should minimize the amount of handling of the damaged pipeline. Furthermore, the method of repairing the pipeline should minimize costs and dependency on vessel motions due to sea conditions, such as heave, roll, or pitch, which can result in a significant amount of standby time and cost.
It is desirable to have a subsea pipe attachment and receiving assembly for use in subsea pipeline repairs which can sever a pipeline at a nominal distance above the seabed to allow the damaged section of pipeline to be removed. It is further desirable to have a subsea pipe attachment and receiving assembly which aligns and manipulates a replacement spool to be installed between the severed ends of the subsea pipeline. Furthermore, the subsea pipe attachment and receiving assembly should be operable with the use of an ROV.